This invention relates generally to rock drills and more particularly to rock drills of either the down hole or out of the hole variety.
At present there are two basic types of drills. The first is the valveless type wherein air pressure to both the drive and return chambers are controlled by the position of the piston. The drill described in U.S. Pat. No. 4,084,646 is a typical example.
The second basic type of drill is the valved type wherein air pressure to both drive and return chambers are controlled by a two position valve. The drill described in U.S. Pat. No. 2,937,619 is an example.
It is desirable in any rock drill to maximize the output power and the efficiency. The most effective way to accomplish this is to optimize the point of admission of air to the drive chamber on the piston upstroke and independently to optimize the point of closing the air supply to the drive chamber on the piston downstroke.
Valveless drills cannot do this because the points of air admission and air closing are tied to the piston position. valved drills cannot do this because they must be open to either the drive or return chamber restricting a more coefficient application of fluid to the two chambers.
The subject invention, by incorporating the conventional valveless construction on the return chamber side and a valve on the drive chamber side which independently controls both air admission and air closing, optimizing power output and efficiency.